This invention relates generally to magnetic tape apparatus, particularly to tape transports for use as peripheral devices or subsystems of computer systems, and more particularly to those for use with two-reel, belt-driven, bidirectional multitrack tape cartridges of the type disclosed in U.S. Pat. No. 3,692,255 filed by Von Behren and assigned to Minnesota Mining and Manufacturing Company, of Minnesota, the United States, although it is not desired that the invention be limited to this particular type of tape assembly. Still more particularly, the invention pertains to a method of, and apparatus for, moving the magnetic transducer or head of such tape transport from a forward track to a reverse track, or vice versa, across the tape of such tape assembly against the risk of damaging the tape in so doing.
The two-reel tape cartridge according to Von Behren employs a flexible belt for bidirectionally driving the tape between a pair of reel hubs. The driving belt extends along a belt guide path around guide rollers adjacent the reel hubs and a belt driving roller therebetween and contacts the tape on the reel hubs. The rotation of the belt driving roller causes the belt to frictionally drive the tape reels to tension the tape and to move the tape between the reels. This cartridge construction offers the advantages of low power bidirectional drive and rapid acceleration and deceleration of the tape by a single reversible drive motor.
There has been a problem, however, that has been left unsolved with the belt-driven bidirectional tape cartridge discussed above. The problem arises from the fact that the tape tension of the cartridge progressively increases with tape travel from one tape extremity to the other in either direction, as has been confirmed by the applicant. Although the reason for this is not necessarily clear, the most reasonable explanation seems to be the change in tape diameters on both reels.
Conventionally, for shifting the magnetic transducer from one forward tack to a reverse one, or vice versa, the tape has been stopped when the transducer has read or write data to the end of a forward or reverse track, and then the transducer has been shifted to a reverse or forward track for reading or writing data thereon. Since the tape tension increases as aforesaid with tape travel from one extremity to the other, the conventional practice has been to shift the transducer across the tape when its tension is the highest. The transducer is customarily configured for smooth travel in the longitudinal, but not transverse, direction of the tape. This transducer configuration has so far been damaging to the tape because the transverse travel of the transducer has taken place when the tape tension is the highest, that is, when the transducer is most strongly pressed against the tape. Similar problems have been encountered with other bidirectional tape assemblies in which tape tension grows higher with tape travel from one extremity to the other.